Electrowinning systems for the recovery of metals from salt solutions are well known. In most systems of this type, the intent is to dispose of spent electrolyte solutions as waste and/or to recover metal value for reuse. In some cases, a limited incidental amount of recovery of acid value is obtained in conjunction with related processes. A procedure is disclosed in U.S. Pat. No. 4,944,851 for the regeneration of a spent tin/lead stripping composition comprising an aqueous solution of an alkanesulfonic acid, metal alkanesulfonate salts and metal nitrate salts by electrolyzing the solution and thus removing certain metal salts at the cathode while regenerating other metal salts along with some acid at the anode. In this system, inorganic nitrate is an essential component of the solution since it is required to act upon the tin-lead layer to effect its removal from the substrate. The procedure described pertains only to the regeneration of stripping capacity in solutions which contain at a minimum both metal alkanesulfonate salts and metal nitrate salts. The objective of the process, as stated by the inventors, is specifically to restore the stripping effectiveness of two-component compositions. The process of the aforementioned U.S. Pat. No. 4,944,851 is not designed to generate sulfonic acid which may have general application in electrolytic and/or other processes as well as in the process from which the sulfonic acid was originally obtained.
U.S. Pat. No. 5,520,794 by Gernon discloses the use of an undivided cell electrowinning process for the recovery of methanesulfonic acid value from a solution of plumbous methanesulfonate. However, when an electrowinning process is carried out, as described by Gernon, in an undivided cell, then the resulting acid product has poor purity owing mostly to contamination by some residue of the metal(s) originally present.
The applications in which such poor purity MSA can be used are usually somewhat restricted.
Vork (Tijdschr. Oppervlaktetech. Corrosiebestrijd. 1995, 39(6), 242-4) discloses the use of an anion-exchange membrane divided electrowinning cell for the recovery of pure methanesulfonic acid from methanesulfonic acid based tin/lead plating solutions. The methanesulfonic acid recovered by Vork was sufficiently pure to be of value for general use, for instance, as an acid catalyst in a number of esterification reactions.
It would be useful to have a general process for obtaining alkanesulfonic acid value and/or pure alkanesulfonic acid from an aqueous solution containing one or more VIB, VIIB, VIII, IB, IIB and/or VA metal alkanesulfonates. Neither such a process nor the possibility for general acid recovery from metal alkanesulfonates are disclosed in the prior art, except for the distinct IVA metal salts tin and lead methanesulfonate.
An element's physical and chemical properties are related to the element's position in the periodic table and since tin and lead are in the same family of the Periodic Table (i.e., the IVA metals) they have certain similarities in physical and chemical properties which are not common to metals outside of group IVA.
Also, in electrowinning processes for the recovery of alkanesulfonic acid value or pure alkanesulfonic acid from aqueous solutions containing metal alkanesulfonates, the specific metal alkanesulfonate involved strongly influences the many operational parameters present (e.g., electrode material selection, membrane selection, membrane fouling prevention schemes, metal hydrolysis accommodation, etc.). Thus, a process designed for tin methanesulfonate and/or lead methanesulfonate does not simply extrapolate to the whole of the periodic table.
Therefore, though it has previously been shown that methanesulfonic acid can be recovered from tin methanesulfonate and lead methanesulfonate under certain conditions, it is not known generally that alkanesulfonic acid can be recovered from other electrodepositable metals (namely metals in groups VIB, VIIB, VIII, IB, IIB and VA).